My wife recently got a new HTC Eris cellphone with Android. It is the first "Smart" phone in the household. Seeing all that it can do along with all the personal information that resides on it, should I be seriously considering some type of security app? with anti-virus or without?

I have glanced at a few along with some comments, but haven't really looked too deep into it. Not too fond of the idea of backing up to their site.

More seriously, your datas are safe as long as you don't install malicious stuff, just like with pc.
Then is the other mater of the phone being lost / stollen. But there, if however find it can find my name to tell where my phone is, i'll be happy.